function get_random() {
    var ranNum= Math.floor(Math.random()*2);
    return ranNum;
}

window.onload=function(){
	var header = document.getElementById("header_random");	
	if (get_random()>=1) {
		header.style.background = "url(images/header.gif) no-repeat";
	} else {
		header.style.background = "url(images/header2.gif) no-repeat";
	}
}